Bags equipped with plastic zippers are widely used for packing materials such as foods, medicines, electronic products and other goods. Especially, bags equipped with plastic zippers fitted with sliders are widely used for packing materials as readily openable and re-sealable packing materials.
When an inside pressure-resistance, i.e., property wherein the bag does not open even if the pressure therein rises, is attached great weight to a bag with a plastic zipper, the plastic zipper which has been disclosed by the present inventor in patent document 1 (Japanese Patent Application Laid-open No. 2000-262307) or patent document 2 (Japanese Patent No. 2938784), or the zipper using the principle of a lever which has been disclosed in patent document 3 (U.S. Pat. No. 5,007,143) or patent document 4 (U.S. Pat. No. 6,293,701) has been known as a plastic zipper with a slider which has a large intensity against opening from a content side of the bag. Although the plastic zipper disclosed in the patent document 2 is itself hermetic, the other plastic zippers disclosed in the other patent documents or conventional plastic zippers do not have hermetic property.
However, with diversification of contents of packages, still more advanced air tightness of package has been required, and a sealed package having been opened by the wrong purpose or by an inaccurate error may cause various troubles such as mixing of foreign substances in the contents of the package or spoiling the quality of contents, and therefore, an additional function that is able to detect the broken seal of the package after sealing the package is desired.
Conventionally known examples of plastic zippers with sliders having functions for detection of broken seal are illustrated in FIGS. 14 to 19. In the example illustrated in FIG. 14, which is a partially sectioned perspective view, and in FIG. 15, which is a sectional view seen in arrow A-A′ in FIG. 14, a bag body 9-3 is fitted with a zipper 9-2 and a slider 9-1, and the slider and the zipper located at the upside portion of the bag body 9-3 are covered by the covering film 9-4 having perforations 9-5. When a new bag is opened in this example, the zipper is opened or closed by the slider after tearing off the perforations 9-5. Therefore, the system is simple and has a good operability. However, there is a disadvantage that the bag has inferior appearance and inferior industrial productivity.
In the example illustrated in FIG. 16, which is a partially sectioned perspective view, and in FIG. 17, which is a sectional view seen in arrow B-B′ in FIG. 16, a bag 9-3 is equipped with a zipper 9-2 and a slider 9-1, and a partitioning film 11-4 equipped with perforations 11-5 is formed inside the bag. In this example, when the pristine bag is opened first, after the zipper 9-2 is opened by the slider 9-1, the perforations 11-5 formed in the partitioning film 11-4 are torn off to open the bag. Accordingly, the bag has a good appearance and productivity. However, when the contents of the bag are fine particles such as powder, there may occur a problem that the fine particles are stuck on the portion of the partitioning film 11-4 and that smooth discharge cannot be performed.
In the example illustrated in FIG. 18, which is a perspective view, a bag 9-3 is equipped with a zipper 9-2 and a slider 9-1, and in the bag body with zipper, spot welding is carried out at an upper portion of the zipper 9-2, while the zipper is put in the closed position. The spot welded portion is cut off by using the slider 9-1 upon first break of seal of a new bag body.
In the example illustrated in FIG. 19 which is a perspective view, the zipper 9-2 disposed on the bag 9-3 is put into a closed state, and the upper part of zipper 14-4 equipped with perforations 14-5 is partially cut out where the slider 9-1 is equipped. In this system, the upper part of the zipper 14-4 is torn out along the perforations 14-5 by means of the slider 9-1 when the seal is broken.
Although the system of FIGS. 14 and 16 has an advantage that it is able to keep air tightness of the bag even if perforations are applied, however, the system of FIGS. 18 and 19 cannot be applied to such usage that requires long preserving period as a retort packed food because the air tightness of this bag depends on the air-tightness of the zipper.
The present inventor disclosed in patent document 5 (WO 02/38459 A1), a plastic zipper fitted with a slider and a bag body equipped with the plastic zipper fitted with the slider, wherein the high air tightness can be achieved so that a long term preservation of contents of the bag becomes possible, while it is readily openable, and it has a function indicating unjust unsealing of the bag. Namely, the objects of the invention was achieved by welding the top portion of the male hook 3-1 and the bottom portion of the female hook 3-2, and in addition, projections for guiding the slider, in the plastic zipper with the slider, respectively, through the readily peelable plastic layers A-1, A-2, A3-5 and A3-6, as illustrated in FIG. 4(a), or welding a continuous pressing rib 1-4 and a continuous tightening wall 1-2 of the plastic zipper with a slider, and in addition, the slider guiding projections G-1 and G-2, respectively, through the readily peelable plastic layers A-2, A-1, A-5 and A-6, as exemplified in FIG. 3 (c), and the resin of the welded portion are made from two different colors.
Although the above mentioned patent document 5 discloses that heat sealing using a hot air nozzle, a heated plate for heat sealing, an ultrasonic welding, a high frequency welding, etc. are available for the method for welding a zipper portion by a readily peelable plastic layer, actually carried out method is not disclosed.
Concerning the way of welding the zipper portion by the readily peelable plastic layer, the following information has been found later as a result of whole hearted study conducted by the present inventor. Although the heat sealing using the hot air nozzle or adhesion using the heated plate has an advantage that it can be applied easily at a low equipment cost, it has a disadvantage that it is hard to uniformly control its welding area or its welding position. Therefore, although the readily peelable plastic layer can be welded, it is difficult to maintain the peeling strength of the readily peelable plastic layer within a certain range. Moreover, if the hook portion of the zipper is heated excessively, it will deform, and then it may cause defects of the zipper function. As a result, since it occurs frequently that the slider operation becomes extremely heavy and that the zipper does not open or not close, there is a precarious situation in industrial production.
When welding is carried out by using high frequency heat sealing, the voltage will rise if the thickness of the zipper is large, and a short circuit may occur between the electrodes, and therefore, an applicable shape of the zipper will be restricted to the thin shaped zipper. Accordingly, the high frequency heat sealing has a problem that it cannot be applied to a thick shaped plastic zipper.
Regarding ultrasonic heat seal, universal welding equipment of batch-wise transfer type has been known wherein a film supplied intermittently in a bag making machine etc. is sandwiched between an ultrasonic horn and an anvil which are vertically movable, and the ultrasonic horn and the anvil are repeated to move in a direction perpendicular to the sealed layer after the film is sealed by means of ultrasonic wave. (For example, patent document 6 (Japanese Patent Application Laid-open No. Hei 9-323708)) Moreover, when a continuously supplied film is welded by means of ultrasonic wave, it is proposed to detect the passing speed of the film and adjust the imposed energy so as to correspond to the passing speed of the film. (Under a low speed, amplitude of an oscillator or pressurization is made small, and under high speed, amplitude of an oscillator or pressurization is increased.) (Patent document 7 (Japanese Patent Application Laid-open No. Hei 11-198233))
However, it has not been known to continuously weld by means of ultrasonic wave while the engaging portions of the plastic zipper are maintained in a stable state wherein the adhesion area and the adhesion intensity are maintained stable in a lengthwise direction for a long distance.
Moreover, any method has not been known wherein the welding is carried out to the specific position of a plastic zipper through the readily peelable plastic layer and wherein the peeling intensity at the welded portion is adjusted to a value in a predetermined range.
Generally speaking the exfoliation performance of readily peelable resin, the adhesion area and the peeling strength will change depending on the welding time, the welding temperature, or the cooling time, even if resin is the same. In the case of adhesion between flat surfaces such as films, any problems hardly arise substantially since a peeling angle (an angle between the exfoliated films upon peeling off) does not change, even if the adhesion area or the peeling strength may change somewhat. However, when the adhesion surface is formed in such a complicated shape as the zipper of the present invention, a relative peeling angle changes sharply responding to minute change of exfoliation area. Consequently, since the nature of exfoliation and the peeling strength have tendency to change sharply, management of the adhesion area or the peeling strength is very important for maintaining the quality of the product, and another technology different from that used for adhesion of films is required.
Moreover, in the patent document 8 (WO 03/022697 A1), the present inventor disclosed a small, powerful slider that is able to open such a hermetic plastic zipper having a strong opening intensity wherein the engaging portions are welded through readily peelable plastic layer.    Patent document 1 Japanese Patent Application Laid-open No. 2000-262307    Patent document 2 Japanese Patent No. 2938784    Patent document 3 U.S. Pat. No. 5,007,143    Patent document 4 U.S. Pat. No. 6,293,701    Patent document 5 WO 02/38459 A1    Patent document 6 Japanese Patent Application Laid-open No. Hei 9-323708    Patent document 7 Japanese Patent Application Laid-open No. Hei 11-198233    Patent document 8 WO 03/022697 A1